One thing to consider is the texture of the plastic, which will show through the paint. Toyota plastics tend to use a fine pebbly texture, and when you paint it the finished product will look more orange-peel than the smoother steel/aluminum stamped parts. It will change the appearance of the gloss, too, looking a bit more flat. You can see the effect on some of the new Tacoma trims with painted fender flares. It's not a big deal for some people. To me it looks like a bad aftermarket finish when a painter doesn't control the atomization well.
Aside from that, the plastic parts should be relatively easy to remove and take to a shop for proper paint application. Done right the paint will be as durable as a painted bumper.